dragons are definitely my favorite pokemon...but dragon teams are severely hard to use due to SR which takes a toll on a majority due to a common flying secondary type which also causes the huge ice weaknesses...if I have to choose some for and OU team, I'd go...
Garchomp- sand veil-life orb
adamant/ jolly, max attack and speed
-EQ
-S-dance
-fire fang
-dragon claw/ outrage
Salamence-intimidate-expert belt
adamant, max attack and speed
-EQ
-d-dance
-fire blast
-dragon claw/ outrage
Milotic-marvel scale-leftovers
calm, max defense and SD
-surf/ scald
-ice beam
-dragon tail
-recover
Hydreigon-levitate-wise glasses/choice scarf
timid, max speed and special attack
-dark pulse
-dragon pulse/ draco meteor
-flamethrower/ fire blast
-surf/ focus blast
Serperior-contrary-leftovers
timid, max speed and SA
-leaf storm
-dragon tail/ dragon pulse (if it gets it in grey)
-leech seed
-hidden power fire
Haxorus-mold breaker-focus sash/ expert belt
adamant, max speed and attack
-dragon claw/ outrage
-d-dance
-EQ
-rock slide
a great substitute for hydreigon would be:
Latios-levitate-choice scarf/ wise glasses
modest, max speed and SA
-draco meteor
-psychic
-grass knot
-shadow ball/ recover
some other good candidates are timid swift swim kingdra with rain dance wher it can be a great counter to all the drizzle-toed teams out there, d-dance gyarados, SR aerodactyl, bulky multiscale dragonite wall with roost, max speed archeops with acrobatics and flying gem, modest choice scarf sceptile, solar power charizard to counter the drought-tales teams and u-turn flygon
also, I occasionally sneak in a lucario since lucario can learn dragon pulse and is also a great counter to ice moves, it's modest, max speed and SA with choice scarf, aura sphere, dark pulse, dragon pulse, and psychic....